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United States Patent |
5,001,438
|
Miyata
,   et al.
|
March 19, 1991
|
Charged particle accelerator and method of cooling charged particle beam
Abstract
A new cavity which is separate from a rf (radio frequency) accelerating
cavity is provided on the orbit of charged particles in a ring-shaped
accelerator, and an external oscillator and a coupled antenna which serve
to excite a rf electromagnetic field in the separate cavity are provided.
Using the external oscillator and the coupled antenna, a deflection mode
which has electric field components in the direction of the central orbit
of the charged particles and in which a magnetic field in a direction
perpendicular to the plane of the central orbit develops on the central
orbit of the charged particles is excited in a beam duct part of the
separate cavity through which the charged particles pass. The resonant
frequency of the deflection mode is set at integral times that of a
fundamental rf mode in the rf accelerating cavity, and the phase
relationship between the rf fields of the rf accelerating cavity and the
separate cavity is so held that, when the rf electric field intensity of
the rf accelerating cavity has a phase of zero, the rf magnetic field
intensity of the separate cavity rises in phase.
Inventors:
|
Miyata; Kenji (Katsuta, JP);
Higuchi; Yoshiya (Hitachi, JP);
Nishi; Masatsugu (Katsuta, JP)
|
Assignee:
|
Hitachi, Ltd. (Tokyo, JP)
|
Appl. No.:
|
397431 |
Filed:
|
August 7, 1989 |
PCT Filed:
|
December 5, 1988
|
PCT NO:
|
PCT/JP88/01225
|
371 Date:
|
August 7, 1989
|
102(e) Date:
|
August 7, 1989
|
PCT PUB.NO.:
|
WO89/05565 |
PCT PUB. Date:
|
June 15, 1989 |
Foreign Application Priority Data
| Dec 07, 1987[JP] | 62-307550 |
Current U.S. Class: |
315/503; 313/11; 315/501 |
Intern'l Class: |
H05H 013/04 |
Field of Search: |
328/233,235,237,228
|
References Cited
U.S. Patent Documents
4780683 | Oct., 1988 | Nakata | 328/235.
|
Foreign Patent Documents |
22400 | Jan., 1987 | JP.
| |
147641 | Jul., 1987 | JP.
| |
287600 | Dec., 1987 | JP.
| |
Primary Examiner: Wieder; Kenneth
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus
Claims
What is claimed is:
1. In a ring-shaped charged particle accelerator having a vacuum vessel in
which a charged particle beam is confined, and which includes therein
bending magnets for deflecting the charge particle beam and forming a
closed orbit of charged particles, focusing magnets for focusing the
charged particle beam, and a rf accelerating cavity for accelerating the
charged particles;
a charged particle accelerator comprising:
a cavity which is separate from said rf accelerating cavity, and
means for exciting a rf electromagnetic field in said cavity separate from
said rf accelerating cavity, in such a manner that the rf electromagnetic
field is established in a deflection mode which has electric field
components in a direction of a central orbit of the charged particles and
in which a magnetic field in a direction perpendicular to a plane of the
central orbit develops on the central orbit of the charged particles, that
a resonant frequency of the deflection mode is set at integral times a
resonant frequency of a fundamental rf mode in said rf accelerating
cavity, and that a phase relationship between high frequencies of said rf
accelerating cavity and said cavity separate therefrom is so held that,
when a rf electric field intensity of said rf accelerating cavity has a
phase of zero, a rf magnetic field intensity of said cavity separate from
said rf accelerating cavity rises in phase.
2. A charged particle accelerator according to claim 1, wherein said cavity
separate from said rf cavity is a cavity in the shape of a rectangular
parallelepiped which has edges perpendicular to the plane of the central
orbit of the charged particles.
3. A charged particle accelerator according to claim 1, wherein said cavity
separate from said rf accelerating cavity is a cavity in the shape of a
cylinder which has its center axis in the direction perpendicular to the
plane of the central orbit of the charged particles.
4. A charged particle accelerator according to claim 1, wherein said cavity
separate from said rf cavity is a cavity in the shape of a cylinder which
has its center axis in the direction of the central orbit of the charged
particles.
5. A method of cooling a charged particle beam in a ring-shaped charged
particle accelerator wherein charged particles are accelerated by a rf
accelerating cavity; characterized in that a cavity separate from said rf
accelerating cavity, and means for exciting a rf electromagnetic field in
the separate cavity are provided, that a deflection mode which has
electric field components in a direction of a central orbit of the charged
particles and in which a magnetic field in a direction perpendicular to a
plane of the central orbit develops on the central orbit of the charged
particles is excited in a beam duct part of said separate cavity through
which the charged particles pass, by the rf electromagnetic field
excitation means, and that a resonant frequency of the deflection mode is
set at integral times a resonant frequency of a fundamental rf mode in
said rf accelerating cavity.
Description
TECHNICAL FIELD
The present invention relates to a ring-shaped accelerator for accelerating
charged particles and a method of cooling a charged particle beam, and
more particularly to an accelerator which is well suited to enter a
particle beam of large current at low energy and then accelerate it to
high energy and to store the high-energy particle beam.
BACKGROUND ART
A diagram of the whole accelerator system is shown in FIG. 2. This
apparatus is constructed of an entrance device 3 which enters charged
particles, and a ring-shaped accelerator 50 which accelerates and stores
the particles. Used as the injector 3 is a linac, a synchrotron, a
microtron or the like. The ring-shaped accelerator 50 includes a beam duct
7 which forms a vacuum vessel for confining a particle beam 2, bending
magnets 5 which deflect the orbit 10 of the particle beam 2, quadrupole
magnets 6 which endow the particle beam with a focusing function, and a rf
(radio frequency) accelerating cavity 4 which accelerates the particles.
For industrializing such an apparatus, it has become an important theme to
reduce the size of the apparatus and yet to permit the storage of a large
current. As one idea therefor, there is a proposal in which particles are
entered at a low energy level below 100 MeV and are accelerated and then
stored. Although there is an actual example having realized the proposal,
a large current of about 500 mA has not been stored in any example yet. By
the way, an apparatus of this type is discussed in, for example,
"Institute of Physics, Conference Series No. 82, p. 80-84 (Cambridge, 8-11
Sept. 1986)".
In the ring-shaped accelerator, the particles circulate while
betatron-oscillating round a closed orbit corresponding to the energy of
the particles. Besides, as shown in FIG. 3, the bunch of particles to be
accelerated have as their central orbit a closed orbit 20 which
corresponds to their center energy. In general, a closed orbit 21
corresponding to energy higher than the center energy lies outside the
central orbit 20, whereas a closed orbit 22 corresponding to energy lower
than the center energy lies inside the central orbit 20. In this manner,
the closed orbits of the particles exhibit energy dispersiveness.
On the other hand, in order to accelerate the bunch of particles, at least
one rf accelerating cavity is disposed on the orbit of the particles, so
that the particles are oscillated also in terms of energy by the
acceleration/deceleration mechanism of a rf electric field based on the
cavity. This phenomenon is usually called "synchrotron oscillations". The
synchrotron oscillations affect the betatron oscillations of the particles
on account of the energy dispersiveness of the closed orbit stated above.
For this reason, the amplitude of the transverse oscillations of the
particles enlarges with the spread of an energy distribution attributed to
the synchrotron oscillations.
Thus, the beam widens greatly in the transverse direction thereof The
widening gives rise to a transverse wake field (a transient
electromagnetic field due to the interaction between the particles and the
wall of the vacuum vessel), and the wake field renders the behavior of the
particle bunch unstable. Heretofore, this phenomenon has led to the
problem that a heavy beam loss arises in the acceleration process of the
particles after the injection thereof, so the storage of the large current
is impossible.
SUMMARY OF THE INVENTION
An object of the present invention is to make the storage of a large
current possible in such a way that the widening of a beam in the
transverse direction thereof is lessened to weaken a wake field in the
transverse direction and to restrain the beam from becoming unstable,
thereby to reduce a beam loss.
In the present invention, in order to accomplish the above object, a new
cavity which is separate from a rf (radio frequency) accelerating cavity
is provided on the orbit of charged particles in a ring-shaped
accelerator, while an external oscillator and a coupled antenna which
serve to excite a rf electromagnetic field in the separate cavity are
provided; using the separate cavity, the external oscillator and the
coupled antenna, a deflection mode which has electric field components in
the direction of the central orbit of the particles and in which a
magnetic field in a direction perpendicular to the plane of the central
orbit develops on the central orbit of the particles is excited in a beam
duct part of the separate cavity through which the particles pass; the
resonant frequency of the deflection mode is set at integral times that of
a fundamental rf mode in the rf accelerating cavity; and the phase
relationship between the rf fields of the rf accelerating cavity and the
separate cavity is so held that, when the rf electric field intensity of
the rf accelerating cavity has a phase of zero, the rf magnetic field
intensity of the separate cavity rises in phase.
According to the present invention, the charged particles induce an intense
synchro-betatron resonance, and the widening of a charged particle beam in
the transverse direction thereof lessens Even in case of low-energy
injection, accordingly, the beam can be restrained from becoming unstable,
and its loss can be reduced, so that the ring-shaped accelerator is
permitted to accelerate and store a large current.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing the situation of the distribution of electric
and magnetic fields in a cavity which serves as the basic element of the
present invention.
FIG. 2 is an arrangement diagram of the whole accelerator system showing an
example of a ring-shaped accelerator to which the present invention is
applied.
FIG. 3 is a diagram showing the situation of the closed orbits of charged
particle beams in mode-like fashion.
FIGS. 4(a)-(d) are diagrams of an analyzed example showing the concrete
effect of the present invention.
FIG. 5 is a diagram of betatron oscillations showing the basic principle of
the present invention.
FIGS. 6(a)-(d) are diagrams showing the first embodiment of the present
invention.
FIG. 7 is a diagram showing the phasic relationship between a rf electric
field intensity and a rf magnetic field intensity.
FIGS. 8(a)-(d) are diagrams showing the second embodiment.
FIGS. 9(a)-(d) are diagrams showing the third embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
First of all, there will be described a (beam cooling) operation in which
the widening of a beam in the transverse direction thereof is lessened by
the present invention.
FIG. 1 illustrates the distribution of electric and magnetic fields in the
cavity of the present invention in the case where bunched particles 2 pass
inside the cavity When the particle bunch 2 passes inside the cavity, it
is affected by the electric and magnetic fields Thus, the amplitude and
phase of betatron oscillations being the transverse oscillations of the
particles change to incur a fluctuation in the circulating period of the
particles. This, in turn, brings about a phase fluctuation in synchrotron
oscillations being the oscillations of the particles in the longitudinal
direction of the beam. An analyzed examples of the behavior of the
particles on this occasion is illustrated in FIG. 4.
Shown in FIG. 4 are variations-with-time in the phase of the synchrotron
oscillations of the particles, the energy deviation, the betatron
amplitude, and the maximum amplitude of the particles with respect to the
central orbit of the particles. The number of circulating turns of the
particles is employed as time coordinates on the axis of abscissas. As
shown in FIG. 4, minute rf oscillations are supersposed on the sinusoidal
curve of the phase of the synchrotron oscillations The frequency of the
minute oscillations agrees with a betatron frequency, and this is based on
the aforementioned phase fluctuation of the synchrotron oscillations
attributed to the betatron oscillations.
On the other hand, low-frequency oscillations at the same frequency as that
of the synchrotron oscillations are superposed on the betatron amplitude.
This is ascribable to the fact tat, owing to the change of the phase of
the synchrotron oscillations, the influence of the electromagnetic field
which the particles undergo in the cavity fluctuates just at the period of
the synchrotron oscillations.
As stated above, the synchrotron oscillations and betatron oscillations of
the particles are intensely coupled by the electromagnetic fields in the
cavity. At this time, the particles exhibit an intense synchrobetatron
resonance, so that as shown in FIG. 4, the synchrotron oscillations and
the betatron oscillations attenuate, and also the maximum amplitude of the
oscillations of the particles with reference to the central orbit
attenuates.
The synchro-betatron resonance mentioned here is different in nature from a
synchro-betatron resonance having heretofore been observed, and a
deflection mode is deeply concerned with the phenomenon. Since the
synchrotron oscillations and the betatron oscillations relate
complicatedly to each other herein, it is difficult to intuitively
understand the essence of the phenomenon. It has been revealed, however,
that a rf magnetic field in the deflection mode plays an essential role in
the phenomenon. Matters close to the fundamentals of the phenomenon will
be briefly explained below.
The syncrho-betatron resonance phenomenon is based on the interaction
between the synchrotron oscillations and the betatron oscillations. In
general, various causes for the interaction are considered, but the
following phenomenon is the main cause here:
As the influence which the betatron oscillations exert on the synchrotron
oscillations, there is that shift of the circulating period which is
ascribable to the betatron oscillations and due to which the phase of the
synchrotron oscillations changes Letting the amount of the phase change be
.DELTA..theta.,
##EQU1##
holds. Here,
h: harmonic number,
L: circumference,
x.sub.o : lateral shift from a closed orbit at a certain observation point,
y.sub.o : .alpha..sub.o x.sub.o +.beta..sub.o x.sub.o ',
x.sub.o ': inclination relative to the closed orbit, of the orbit of
particles at the same observation point as that of x.sub.o,
##EQU2##
S=sin.mu.
C=1-cos.mu.
.alpha..sub.o, .beta..sub.o : Twiss parameters at the same observation
point as that of x.sub.o,
.eta..sub.o : energy dispersion value at the same observation point as that
of x.sub.o,
.xi..sub.o =.alpha..sub.o .eta..sub.o +.beta..sub.o .eta..sub.o '
.mu.=2.pi..nu.(.nu.=betatron tune)
The observation point in Eq. (1) is set at a position lying directly behind
the cavity of the persent invention. Then, .DELTA..theta. is an evaluation
formula for that shift of the phase of the synchrotron oscillations which
arises in a path from the observation point to a position lying directly
before the cavity of the present invention, and the influence of a rf
electric field in a rf accelerating cavity is not contained in the formula
Of course, the above influence is taken into consideration in a numerical
simulation, but note shall be taken of only the influence of the rf
magnetic field in the cavity of the present invention here.
As indicated by Eq. (1), the shift .DELTA..theta. of the phase of the
synchrotron oscillations relates linearly with x.sub.o and y.sub.o. For
this reason, when the phase shift is considered on an x.sub.o -y.sub.o
plane, the signs of .DELTA..theta. differ at a point (x.sub.o, y.sub.o)
and a point (-x.sub.o, -y.sub.o). Therefore, the minute phase oscillations
corresponding to the betatron oscillations are superposed on the
synchrotron oscillations. Considering that the intensity of the rf
magnetic field in the cavity of the present invention changes versus the
phase of the synchrotron oscillations, the particles behave on the x.sub.o
-y.sub.o plane as depicted in FIG. 5. This figure shows an example in
which the fraction of the betatron tune .nu. is near 0.25. As illustrated
by the figure, the deflection angles of the particles by the rf magnetic
field differ at individual points (x.sub.o, y.sub.o), so that the amounts
of changes of y.sub.o differ at the respective points, and this gives rise
to the attenuation of the amplitude of the betatron oscillations.
Now, the first embodiment of the present invention will be described with
reference to FIGS. 6(a)-(d). In the ring-shaped accelerator as shown in
FIG. 2, a cavity 1 in the shape of a rectangular parallelepiped as shown
in FIG. 6 is installed on the particle orbit 10 separately from the rf
accelerating cavity 4, so as to pass the particle beam 2 inside the cavity
1. As illustrated in the drawing, rectangular coordinate axes x, and y and
z are taken, and an x-z plane is set as the plane of the orbit of the
particle beam, a z-direction as the traveling direction of the particle
beam an x-direction as the outer direction of the ring relative to the
particle beam, and a y-direction as a direction perpendicular to the plane
of the particle beam orbit. The center axis of the cavity 1 is determined
so as to agree with the closed orbit (central orbit) corresponding to the
center energy of the particle beam 2.
A microwave is injected from an external oscillator 100 into the cavity 1
through a coupled antenna 101, and a rf electromagnetic field of
TM.sub.210 mode is established in the cavity 1 as shown in the drawing.
The resonant frequency of the electromagnetic field oscillations is set at
integral times (m times) the acceleration frequency of the particles (the
resonant frequency of the fundamental acceleration mode of the rf
accelerating cavity 4). On this occasion, the relative phases of the
electromagnetic modes of both the cavities are set as shown in FIG. 7. In
FIG. 7, numeral 91 indicates the rf electric field intensity within the rf
accelerating cavity 4, numeral 92 the rf electric field intensity within
the cavity 1, and numeral 93 the rf magnetic field intensity in the cavity
1. In terms of formulas, the following holds:
V.sub.1 =V.sub.1 osin.theta. (2)
V.sub.2 =V.sub.2 ocos(m.theta.) (3)
Here,
V.sub.1 : voltage within the rf accelerating cavity 4,
V.sub.2 : voltage in the cavity 1,
.theta.: rf phase,
V.sub.1 o: amplitude value of V.sub.1, V.sub.2 o: amplitude value of 2.
At this time, the particles induce the intense synchrobetatron resonance as
stated before, and the transverse beam size lessens.
Here, the integer m is determined from the viewpoint of the size of the
cavity 1 coming from the resonant frequency of the deflection mode in the
cavity. Usually, the resonant frequencies of rf accelerating cavities are
broadly classified into a 100 MHz-band and a 500 MHz-band m=4-5 is set for
the 100 MHz-band, and m=1 is set for the 500 MHz-band, whereby the
resonant frequency of the deflection mode in the cavity 1 is adjusted to
or near 500 MHz. Thus, the cavity 1 becomes a size suited to the
accelerator. The size will be concretely estimated. The electromagnetic
resonance mode in the cavity 1 shall be approximated by one in the absence
of the beam duct 7. In FIG. 6(d), the lengths of the cavity in the x-, y-
and z-directions are let be a, b and l, respectively. Then, the resonant
frequency f.sub.rl of the TM.sub.210 mode being the electromagnetic
resonance mode on this occasion can be expressed as:
##EQU3##
Here, c denotes the velocity of light in vacuum. Assuming a=b, for
example, a=b=67 cm holds for the resonant frequency f.sub.rl =500 MHz, and
these lengths are suitable. The dimension 1 of the cavity in the
z-direction, namely, in the traveling direction of the particle beam 2 is
not determined by the resonant frequency f.sub.rl, and it can be properly
determined considering other factors.
Meanwhile, the magnitude of the rf voltage V can be estimated as follows.
Now, let's suppose the acceleration of the particles in which the energy
(center energy) of the particles traveling along the central orbit is a
low energy level of 10 MeV. The energy distribution of the bunch of
particles is regarded as the Gaussian distribution, and the standard
deviation .sigma..epsilon. thereof is assumed to be 1% of the center
energy of 10 MeV, namely, to be 100 keV. Assuming the synchrotron tune
.nu. (synchrotron oscillation frequency/circulating frequency of the
particles) to be 5.times.10.sup.-3 (in general, considerably smaller than
1), the rf voltage V around the particle beam 2 is, at most:
##EQU4##
Here, e denotes the electric charge of the single particle. The maximum rf
voltage V.sub.m in the cavity 1 can be estimated as:
##EQU5##
Therefore, assuming r.sub.b =3 cm, the following holds by the use of a=67
cm:
##EQU6##
By the way, in the analyzed example of FIG. 3, V.sub.m =-1.0 kV holds for
the rf accelerating voltage V.sub.1 o=5 kV and the synchrotron tune
.nu.=3.6.times.10.sup.-3. When this voltage value is applied to the
Kilpatrick formula of electric discharge limitation, electric discharge
take place for 1{0.05 mm, and the electric discharge is not apprehended as
long as the cavity is fabricated with 1 set in the order of 1 cm.
According to this embodiment, the cavity whose dimensions a and b are about
70 cm and whose dimension 1 is several cm suffices, and a radiant light
apparatus can be held compact.
The second embodiment of the present invention will be described with
reference to FIGS. 8(a)-(d). Incidentally, FIGS. 8(a)-(b) show the
intensity distributions of an electric field and a magnetic field on an
A--A' plane in FIG. 8(c), respectively. This embodiment is such that a
cavity 11 in the shape of a cylinder is employed instead of the cavity 1
in the first embodiment, and that the particle beam is passed penetrating
the side wall of the cylindrical cavity. Coordinate axes are taken in the
same way as in the foregoing, and the cylinder axis of the cavity 11 is
brought into agreement with the z-direction. A microwave is injected from
an external oscillator 100 into the cavity 11 through a coupled antenna
101, whereby a rf electromagnetic field of TE.sub.011 mode is established
in the cavity 11 as illustrated in the drawing. Here, the resonant
frequency f.sub.r2 of the electromagnetic field oscillations of the
TE.sub.011 mode is set at integral times the acceleration frequency of the
particles. The phase relations with the rf accelerating voltage conform
for Eqs. (2) and (3) mentioned before. Also with this embodiment, the same
functional effects as stated in the first embodiment are achieved.
Also here, the dimensions of the cavity 11 and the rf electric field
intensity as required will be concretely estimated.
The radius of the cylindrical cavity 11 is denoted by R, and the height
thereof by h (refer to FIG. 8(d)). The resonant frequency f.sub.r2 of the
TE.sub.011 mode in the cavity 11 can be approximately expressed as:
##EQU7##
Here, j.sub.01 indicates the first zero point of the derivative of the
Bessel function of order O.
Assuming f.sub.r2 =500 MHz and 2R=h by way of example, j.sub.01 =3.83 is
obtained, and hence, h=2R=79 cm holds, so that no problem exists in
realizability.
The required rf electric field intensity becomes as follows: When the value
of the intensity at a point P in FIG. 8(c) is denoted by E.sub.b and the
effective distance of an electric field acting in the traveling direction
of the particle beam 2 is supposed nearly equal to the radius r.sub.b of
the particle beam 2, the rf voltage V is:
V.apprxeq.E.sub.b r.sub.b .apprxeq.500 (V)
Accordingly, Eb.apprxeq.17 kV/m is conjectured subject to r.sub.b =3 cm.
The peak value E.sub.m of the electric field intensity in FIG. 8(a) is:
##EQU8##
which is a sufficiently realizable numerical value. Since, in this case,
the electric field on the wall surface of the cavity is zero, the electric
discharge is not apprehended at all.
Lastly, the third embodiment will be described with reference to FIGS.
9(a)-(c). Incidentally, FIGS. 9(a)-(b) show the intensity distributions of
an electric field and a magnetic field on a B--B' plane in FIG. 9(c),
respectively. This embodiment is such that, as illustrated in FIG. 9(c), a
cavity 31 in the shape of a cylinder is located so as to be penetrated by
the particle beam 2, and that the orbital axis of the center energy of the
particle beam 2 is held in agreement with the center axis of the cavity
31. Coordinate axes are taken in the same way as in the foregoing. A
microwave is injected from an external oscillator 100 into the cavity 31
through a coupled antenna 101, whereby a rf electromagnetic field of
TM.sub.111 mode is established in the cavity 31. Also here, the resonant
frequency f.sub.r3 of the electromagnetic field oscillations of the
TM.sub.111 mode is set at integral times the acceleration frequency of the
particles. The phase relations with the rf accelerating voltage conform to
Eqs. (2) and (3) mentioned before. Also with this embodiment, the same
functional effects as stated in the first embodiment are achieved.
Also here, the dimensions of the cavity 31 and the rf electric field
intensity as required will be confretely estimated.
The radius of the cylindrical cavity 31 is denoted by R, and length thereof
by h (refer to FIG. 9(d)). The resonant frequency f.sub.r3 of the
electromagnetic field oscillations of the TM.sub.111 mode can be expressed
as:
##EQU9##
Here, j.sub.11 indicates the first zero point of the derivative of the
Bessel function of order 1. Assuming f.sub.r3 =500 MHz and 2R=h by way of
example, j.sub.11 =3.83 is obtained, and hence, h=2R=79 cm holds, so that
no problem in realizability exists as in the second embodiment.
The required rf electric field intensity becomes as follows: When the value
of the intensity at a point Q in FIG. 9(c) is denoted by E.sub.b, the
effective distance of an electric field acting in the traveling direction
of the particle beam 2 is h/2 or so, and hence, the rf voltage V is:
##EQU10##
Accordingly, E.sub.b .apprxeq.1.3 kV/m is conjectured subject to h =79 cm.
The peak value E.sub.m of the electric field intensity in FIG. 9(a) is:
E.sub.m .apprxeq.2E.sub.b .apprxeq.2.6 kV/m
which is also a sufficiently realizable numerical value, and the electric
discharge is not apprehended.
According to the present invention, the transverse beam size of a particle
beam entered into a ring-shaped accelerator can be lessened to about 1/10
of the transverse beam size in the prior art, and hence, a transverse wake
field weakens, the beam is restrained from becoming unstable, and the loss
of the beam is reduced, whereby the particle beam of low energy and large
current is permitted to be injected, accelerated and stored. Thus, a beam
injector may be simple, and the whole synchrotron radiation sources for
industrial use can be made smaller in size.
Moreover, according to the present invention, many times of injections at
low energy as have heretofore been impossible become possible, and a large
current injection is facilitated.
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